Recently, there has been introduced a LTE (Long Term Evolution) as a new mobile terminal communication standard. In the LTE, a conventional line switching function (voice calling function) is not provided.
Thus, when the mobile terminal having a LTE function is present in a 3G (3rd Generation) mobile network (mobile phone line) and a voice call is received by the mobile terminal, a technology for switching the reception of the voice call from the LTE network to the 3G network to achieve voice calling may be used (e.g., refer to Nonpatent Literature 1). The same technology may be used when a voice call is made from the mobile terminal This switching is referred to as CSFB (Circuit Switched FallBack).
Recently, there has been developed a 3G femto base station that is a 3G femto cell (femto area) having a communication area narrower than that of a general 3G wireless base station. The 3G femto base station is a compact wireless base station generally having the range of a radius of several tens of meters set as a communication area and installed indoors, for example, in an office.